Biological samples generally consist of complex mixtures of components that include both hydrophobic and hydrophilic compounds of interest. One method that has been adopted to separate and pre-concentrate these types of components is based on the use of spots of affinity materials with differing affinities for hydrophobic, hydrophilic, charged and uncharged compounds, on the surface of a planar platform, typically a plate. This plate is designed to be compatible with a mass spectrometric system that can interrogate the constituents which become concentrated on the surface of such spots. The surface spots attract constituents due to hydrophobic, hydrophilic, charge transfer, ionic, metal-chelate affinity and dye-affinity interactions and each spot has a different composition designed to use one example of such interactions (see e.g. U.S. Pat. No. 7,183,544)
In practice, a solution of the mixture of analytes within a biological matrix which is, for example, serum, plasma, saliva, or urine, is applied to the surface of the plate where selective binding takes place at one or more spots during an incubation step. The plate is then washed to remove unbound constituents and following drying, the plate is interrogated via the mass spectrometer to produce ions which are then identified via their time of flight/charge to mass ratio within the mass spectrometer. The pattern of distribution that is seen for particular chemicals/biochemicals can be used for diagnostic purposes to identify particular diseases, or for other applications.
A method of analysing constituents of fingerprints using MALDI-TOF-MS is disclosed in WO2007/017701. The particles used in the methods are hydrophobic silica particles which are capable of hydrophobic-hydrophobic interactions with a class of constituents. However, the particles disclosed in WO 2007/017701 tend not to be suited for use in analysing constituents which are not capable of hydrophobic-hydrophobic interactions, for example, peptides or amino acids.
In some embodiments, the method of the present invention enables analysis of a wider range of constituents than the prior art using a mass spectrometric technique.